Cognitive ability is poorer among those who start smoking young.

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Smoking marijuana regularly before the age of 16 causes changes in the brain that can impair a young person’s ability to focus, learn from mistakes and think abstractly, according to a Harvard study.

On brain scans, the youngest pot smokers showed activation in regions of the brain that was not seen in those who started smoking after age 16, suggesting early exposure causes neural changes, researchers at Harvard-affiliated McLean Hospital found. Early and habitual users performed more poorly on tests of cognitive functions, including mental flexibility.

Research on how marijuana changes a developing brain is important as it’s the most frequently used illegal drug in the U.S., said study author Staci Gruber, director of the neuroimaging center at McLean Hospital in Belmont, Mass.

Almost 16 percent of eighth-graders have tried marijuana, and that number rises to 42 percent by 12th grade, a 2009 study from the National Institute on Drug Abuse found.

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Early chronic users “make repetitive incorrect responses despite the fact I’m telling them they’re wrong,” said Gruber, also an assistant professor of psychology at Harvard University. “That’s called ‘cognitive inflexibility,’ and you see it in babies.”

The research, presented Monday at the Society for Neuroscience’s meeting in San Diego, also found that the group that started earlier smoked more pot more often than those who started later. People who began smoking before age 16 had 25.1 smokes a week, compared with 12.1 in those who began later. The first group smoked almost three times as many grams a week, Gruber said.

The study compared 33 marijuana smokers to 26 healthy controls. Participants were given tests to measure executive function, a term for brain processes responsible for abilities and behaviors involving abstract thinking, decision making, cognitive flexibility and correcting mistakes.

The results showed those who started using pot before age 16 made twice as many mistakes on tests of executive function as those who began later. The research didn’t examine those people who had started smoking early and stopped, although those people begin to look more like nonsmokers in other studies, Gruber said.

Teens’ video games

not big health threat

HARTFORD, Conn. — The good news is that not only do video games pose little in the way of health hazards for most teens, they’re even linked to lower smoking.

The bad news is that a small group of adolescents are “problem gamers,” and that can lead to trouble.

So says a new study out of Yale, published Monday in the journal Pediatrics. The study has been called one of the most comprehensive examinations of video games’ effect on adolescents’ health.

Of the 4,028 surveyed, 51 percent played video games (76.3 percent male, 29.2 female). The researchers — led by Rani Desai, associate professor of psychiatry and epidemiology at Yale — believe video games pose little concern for adolescents. Among boys, video games are even linked to a lower chance of taking up smoking.

However, a small group of those surveyed (close to 5 percent) reported that they have trouble cutting back on their playing, and feel tense if they don’t play. It’s among this group that problems emerge. Cigarette smoking, drug use, depression and serious fights were found to be more common in this group, for both boys and girls.

The Hartford Courant

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